# Leetcode 2544: Alternating Digit Sum Solution

Here, we will see how to solve Alternating Digit Sum Solution of leet code 2544 problem.

You are given a positive integer `n`. Each digit of `n` has a sign according to the following rules:

• The most significant digit is assigned a positive sign.
• Each other digit has an opposite sign to its adjacent digits.

You have to return the sum of all digits with their corresponding sign.

Example 1:

```Input: num = 123
Output: 2
Explanation: (+1) + (-2) + (+3) = 2```

Example 2:

```Input: num = 886996
Output: 0
Explanation: (+8) + (-8) + (+6) + (-9) + (+9) + (-6) = 0.```

## Alternating Digit Sum Solution in C++:

Here, we will be solving problem in multiple ways with code.

C++ code 1:

```class Solution {

public:

int alternateDigitSum(int n) {

int k = 1, ans = 0;

while(n>0)
{

ans += (n%10) * k;

n = n / 10;

k *= -1;

}

return -k * ans;

}
};
```

C++ code 2:

```class Solution {

public:

int alternateDigitSum(int n) {

int total_digit = 0, tmp = n, sign, sum = 0;

while(tmp) {

total_digit += 1;

tmp /= 10;

}

if (total_digit % 2 == 1) {

sign = 1;

} else {

sign = -1;

}

while(n) {

sum += (n % 10) * sign;

n /= 10;

sign *= -1;

}

return sum;

}

};
```

Output:

```Input: n = 111
Output: 1
Explanation: (+1) + (-1) + (+1) = 1.```

Time complexity: O(n)

Space complexity: O(1)

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Posted in C++, Easy, Leetcode